1. Field of the Invention
This invention relates to the shaping of glass sheets to be laminated, and, in particular, relates to the simultaneous shaping of a pair of glass sheets having a non-rectangular outline of non-uniform curvature in plan by a combination of gravity sag bending and press bending to a complicated shape including a longitudinal bend about a transverse axis of curvature and a complicated bend containing both convex and concave elements in elevation about a longitudinal axis. The bending to such complicated shapes requires that the glass sheets be supported in precise alignment with each of the molds used to impart the different components of the complicated bend to which the glass sheets are to be shaped. Such complicated shapes are required to enable the shaped glass sheets to be mounted in a curved mounting frame forming part of an automobile body so that the curved glass forms a laminated window that merges with the shape of the curved mounting frame and the vehicle body in which it is mounted.
2. Description of Patents of Interest
U.S. Pat. No. 2,131,873 to Goodwillie sag bends a glass sheet to an upward facing shaping surface of a mold of solid continuous extent mounted on a car that moves on wheels riding on fixed rails through a furnace and then stops in alignment below a press bending mold of complementary shape. No specific means is shown to insure proper mold alignment for press bending even though the desirability of proper alignment is mentioned. Hence, this apparatus is limited to shaping glass sheets to simple bends, such as cylindrical or spherical bends, where some misalignment can be tolerated, because of the uniform curvature of the bent sheets.
U.S. Pat. No. 2,442,242 to Lewis discloses apparatus for bending rectangular glass sheets to a cylindrical curvature. The sheets have a straight leading edge that abuts a rib to align a sheet between a pair of heated pressing molds. Fingers that support the sheet during its entry into a position between the pressing molds are retracted from between the pressing molds so that the glass sheet sags toward the lower pressing mold and its shape is completed by pressure between the molds. Only glass sheets having straight leading edges can be aligned between the pressing molds in this patent.
U.S. Pat. No. 2,570,309 to Black sag bends a single glass sheet to conform to the contour of a circular metal outline mold, then lifts the sag bent glass sheet on a concave pressing mold toward an upper convex pressing mold of complementary shape to complete the bending. The press bent glass sheet is lowered to the circular outline mold for transfer to a cooling station. No alignment means is provided to insure that the circular outline mold stops in proper alignment between the pressing molds. Hence, the apparatus of the Black patent is practical only for fabricating glass sheets of circular outline to shapes where misalignment does not result in failure to be able to match the shape of the glass sheet with that of the frame in which the bent glass is to be installed.
U.S. Pat. No. 3,068,672 to Black discloses a sectionalized outline metal mold for bending a glass sheet of non-rectangular outline to a non-uniform shape about a transverse axis of bending by gravity sagging. Stops are provided to guide the location of the glass sheet in proper orientation and alignment relative to the mold. The stops remain in place when the bent glass is removed from the mold. No means is provided to correct the uncontrolled sag in the unsupported region of the shaped glass sheet.
U.S. Pat. No. 3,208,839 to Nordberg press bends glass sheets using a parting agent of colloidal alumina or colloidal silica on the press face to facilitate removal of the bent glass sheet from the mold faces. Only press bending is used to shape the glass.
U.S. Pat. No. 3,251,672 to Touvay et al suggests press bending two tong-suspended glass sheets simultaneously before lamination. No means is provided to avoid tong marks in the glass sheets so treated.
U.S. Pat. No. 3,408,173 to Leflet discloses bending and tempering a glass sheet while supported on an outline mold shaped to have upwardly directed shaping surfaces curved convexly in elevation in one direction and curved concavely in elevation in another direction to impart a complicated shape to a glass sheet so that it is curved convexly in elevation in its longitudinal dimension and curved concavely in elevation in its transverse dimension. No press bending is suggested to minimize uncontrolled sag bending in the unsupported glass sheet area within the mold outline.
U.S. Pat. No. 3,453,161 to Golightly discloses bending at least two glass sheets simultaneously on an outline metal mold of skeleton configuration to bend glass sheets for subsequent lamination in pairs. No press bending to minimize uncontrolled sag is suggested in this patent.
U.S. Pat. No. 3,476,540 to Ritter, Carson and Hymore shapes individual glass sheets conveyed on rollers to a shaping station where each sheet in turn is lifted sufficiently rapidly by an outline mold consisting of a plurality of shaped bars to shape the glass by a so-called inertia gravity bending method.
U.S. Pat. No. 3,554,724 to Ritter and Hymore combines the inertia gravity bending method of the previous patent with peripheral engagement against a supplemental shaping surface constructed and arranged to be contacted by the upper surface of the glass sheet when the latter is lifted. Neither of these last two patents contain any provision for correcting unwanted sag within the supported margin.
U.S. Pat. No. 3,701,643 to Frank discloses apparatus to orient and align moving glass sheets by engaging their opposite side edges. The glass sheets ride over conveyor rolls and their lower major surfaces mar on sliding against the rolls and edge distortion may occur when moving alignment members engage the glass edges.
U.S. Pat. No. 3,778,244 to Nedelec bends glass sheets in a series of pneumatic steps or a combination of a pneumatic step followed by a mechanical step. The patent states that the invention allows to bend two sheets together instead of one on the same apparatus without having to change any step of the process even when the sheets have to be sharply bent. However, no specific way is disclosed in this patent how two sheets can be handled simultaneously by pneumatic handling. Only one sheet may be held by a single suction device.